1. Field of the Invention
This invention relates to a thermoset polymeric composition derived from an ethylenically unsaturated ester or polyester resin monomer. More particularly, the invention relates to such compositions resulting from the incipient addition polymerization or copolymerization product of said resin monomer reacting with a polyisocyanate in the presence of a bicyclic amide acetal monomer.
2. Overview of the Prior Art
Polyester resinous compositions; i.e., ethylenically unsaturated polyester oligomers dissolved in a reactive diluent in the form of a vinyl monomer cross-linking agent, typically styrene, are most extensively used at present for preparing thermoset molded shapes. On balance the physical strength properties of such products are very good. However, for many end use applications the inherent brittleness of the resultant polymeric structure represents a definite drawback. The most satisfactory way to date for obviating this deficiency calls for employing a fibrous reinforcer. Glass fibrous materials in a variety of forms are most commonly resorted to for this purpose. There have been proposals for coping with the inherent brittleness of a cured polyester resinous composition through the conjoint use of a compatible thermoplastic polymer exhibiting an elastomeric property. The disadvantage of this approach is that invariably other desirable physical strength characteristics as well as certain chemical properties are undesirably compromised.
One of the more recent endeavors to upgrade the properties of a conventional polyester resinous composition is exemplified in U.S. Pat. No. 4,374,229. Therein the polyester entity of the contemplated systems is in the form of at least two ethylenically unsaturated oligomeric polyester segments joined together via a urethane linkage. Such polyester entities beyond containing the urethane linking residues additionally contain at least two acryloyl groups as part of their ethylenic unsaturation. A number of significantly improved chemical properties are evident upon the curing of such systems. On the other hand, the gains realized in physical strength properties are more modest. While dimensional stability as measured by higher heat distortion temperatures as well as fatigue resistance were improved, the impact resistance properties are of such an order allowing for only a minor reduction of the reinforcement content normally required for any given application. It is accordingly the principal object of this invention to structurally modify the aforesaid and like polymeric systems in order to obtain improved impact resistance without sacrifice of the other chemical and physical strength properties associated with same.